1. Field of the Invention
The present invention relates to a method for structuring a comparative reference value used to estimate a residual charge (SOC; State of Charge) of a battery, and more particularly to a method for structuring a comparative reference value capable of estimating a SOC of a battery more correctly using a discharge capacity counting (Ah counting) and an open circuit voltage (OCV) hysteresis depending on temperatures.
2. Description of the Prior Art
An electric vehicle uses electric energy stored in a battery as an energy source. A lithium-ion polymer battery is much used as the battery for the electric vehicle, and a research thereof has been also actively carried out.
In the mean time, since a gasoline vehicle drives an engine using the fuel, it is not difficult to measure an amount of the fuel. However, in case of the electric vehicle, it is difficult to measure residual energy accumulated in the battery. In the mean time, it is very important for a driver of the electric vehicle to know the information about how much the energy remains and to what extent the driver can drive.
In other words, since the electric vehicle is driven with the energy stored in the battery, it is very important to perceive the residual capacity of the battery. Accordingly, many technologies have been developed which measure the SOC of the battery during the traveling to notify the driver of the information about the possible distance covered.
In addition, many attempts have been also performed which properly set an initial value of the SOC of the battery before the traveling. At this time, the initial value of the SOC is set with reference to an open circuit voltage (OCV). In this method, the initial value is set on condition that the OCV is not changed depending on the environments and is an absolute reference value of the SOC.
However, according to many tests and theses, it has been proved that the OCV is changed depending on the temperatures and the aging, instead of having a fixed value irrespective of the environments. However, according to the conventional methods of setting an initial value of the SOC of the battery, it is not considered that the OCV is changed depending on the temperatures. Accordingly, the conventional methods cannot accurately estimate the SOC of the battery.
In the mean time, the SOC of the battery includes the discharge capacity counting having a current loss added thereto. Accordingly, it is very difficult to obtain a reference value of a comparison object thereof unless the current applied to the battery is correctly measured. In particular, in case of a battery exhibiting a dynamic pattern, an error thereof is varied depending on an error of a measuring apparatus and an environment of a measurement place, so that it is not easy to obtain a reference value thereof. Accordingly, an open circuit voltage after the battery is sufficiently relaxed is used as the reference value. However, this method can be applied to a battery exhibiting a static pattern. In other words, it cannot be applied to a battery exhibiting a dynamic pattern.